Neutrophil string formation: hydrodynamic thresholding and cellular deformation during cell collisions.

Area of Science:

• Immunology
• Biophysics
• Cell Biology

Background:

• Neutrophils display flow-enhanced adhesion, known as hydrodynamic thresholding, in various assays.
• The efficiency of neutrophil collisions and adhesion under flow conditions is crucial for immune responses.

Purpose of the Study:

• To investigate the mechanism of hydrodynamic thresholding in neutrophil-neutrophil interactions.
• To determine the role of L-selectin and beta(2)-integrins in neutrophil adhesion and string formation.
• To explore calcium mobilization as a mechanosensing response in neutrophils.

Main Methods:

• Utilizing flow assays to measure primary collision efficiency and collision lifetimes.
• Employing high-resolution imaging to observe neutrophil deformation during collisions.
• Using antibodies to block specific cell adhesion molecules and assess their impact.
• Analyzing secondary capture events and firm arrest on ICAM-1 and fibrinogen surfaces.
• Monitoring calcium mobilization in neutrophils.

Main Results:

• Primary collision efficiency showed a maximum at a wall shear rate of 100 s(-1), indicating hydrodynamic thresholding.
• L-selectin antibodies significantly reduced collision efficiency, while antibodies against CD11a, CD11b, or CD18 had no effect.
• Neutrophil-neutrophil string formation was observed on ICAM-1 but not on fibrinogen, peaking at 100 s(-1).
• Neutrophils exhibited significant deformation during collisions at venous shear rates.
• Neutrophils mobilized calcium upon adhesion, string formation, and subsequent flow onset, suggesting mechanosensing via beta(2)-integrin.

Conclusions:

• Hydrodynamic thresholding influences neutrophil string formation, with L-selectin playing a key role.
• ICAM-1 supports neutrophil string formation and firm arrest, unlike fibrinogen.
• Neutrophil deformation and beta(2)-integrin-mediated mechanosensing are critical in adhesion dynamics.